DISTANCE AND DIMENSIONS OF THE SUN. 417 



This mass, if we express it in pounds or tons, is too enormous to 

 be conceived : it is 2 octillions of tons that is, 2 with 27 ciphers 

 annexed; it is nearly 750 times as great as the combined masses of 

 all the planets and satellites of the solar system and Jupiter alone 

 is more than 300 times as massive as the earth. The sun's attractive 

 power is such that it dominates all surrounding space, even to the 

 fixed stars, so that a body at the distance of our nearest stellar neigh- 

 bor, a Centauri, which is more than 200,000 times remoter than the 

 sun, could free itself from the solar attraction only by darting away 

 with a velocity of more than 300 feet per second, or over 200 miles 

 an hour ; unless animated by a greater velocity than this, it would 

 move around the sun in a closed orbit an ellipse of some shape, or 

 a circle, with a period of revolution which, in the smallest possible 

 orbit, would be about 31,600,000 years, and if the orbit were circular, 

 would be nearly 90,000,000. We say it would revolve thus that is, 

 of course, unless intercepted or diverted from its course by the influ- 

 ence of some other sun, as it probably would be. And we may notice 

 here that in many cases certainly, and in most cases probably, the 

 stars are flying through space at a far swifter rate, with velocities of 

 many miles per second. 



If we calculate the force of gravity at the sun's surface, which is 

 easily done by dividing its mass, 325,600, by the square of 108f (the 

 number of times the sun's diameter exceeds the earth's), we find it 

 to be 27-^ times as great as on the earth; a man who on the earth 

 would weigh 150 pounds, would there weigh nearly two tons ; and, 

 even if the footing were good, would be unable to stir. A body 

 which at the earth falls a little more than 16 feet in a second would 

 there fall 443. A pendulum which here swings once a second would 

 there oscillate more than five times as rapidly, like the balance-wheel 

 of a watch quivering rather than swinging. 



Since the sun's volume is 1,280,000 times that of the earth, while 

 its mass is only 325,600 times as great, it follows at once that the 

 sun's average density (found by dividing the mass by the volume) is 

 only about one-quartet- that of the earth. This is a fact of the utmost 

 importance in its bearing upon the constitution of this body. As we 

 shall see hereafter, we know that certain heavy metals, with which 

 we are familiar on the earth, enter largely into the composition of the 



and r the mean radius of the earth ; T, the length of the sidereal year, reduced to seconds ; 

 and \ g the distance a body falls in a second at the earth's surface. Now, the distance 

 the earth falls toward the sun in a second, or the curvature of her orbit in a second, is 



2:r 2 R 2*-' 2 R m M 



equal to -^ (about 0.119 inch). Hence, by the law of gravitation, g : - a H ' -oi 



( 47r ' 2Ra ^ 

 \ T 2 r*g /' 



whence, M = m 



- ,, g 



In this formula make it = 3.14159 ; R, 92,250,000 miles ; T = 31,558,149.3 seconds ; 

 r = 3,956.179 miles ; and g = 0.0061035 mile (16.113 feet), and we shall. get the result 

 given m the text, viz., M = 325,600 m. 

 vol. x. 27 



